The purpose of this study is to determine the prevalence and epidemiologic correlates of C. pneumoniae infection by polymerase chain reaction (PCR) detection in patients with coronary heart disease (CID) compared with normal controls, and to examine the role of C. pneumoniae in the development of allograft vasculopathy in heart transplant recipients. Evidence is rapidly accumulating to support a role for Chlamydia pneumoniae in the development of atherosclerosis (1,2). This appears to be mediated through an inflammatory process as a result of chronic host-pathogen interaction. C. pneumoniae infects pulmonary alveolar macrophages and is then hematogenously disseminated by infected macrophages (3). It is thought to establish a persistent infection of vascular tissues and to stimulate atheroma formation by changing the local cytokine milieu. (continued)